I’m on a long climb somewhere in the north of Spain, and my team director is screaming in my earpiece. It’s a big, nasty mountain pass, and the lead racers are flying up the road without me. I’ll really need to push myself to stay with these guys.

“Vengavengavengaaaa.”

I grab the center of the handlebar and lower my head. My legs burn like I just received a transfusion of hot drain cleaner.

The director is in a frenzy. He pulls up beside me, leans out the car window, and starts making karate-chop motions at my legs, as if trying to frighten them into spinning faster. “Let’s goooo!!” he shrieks. “Come on! You are almost at the top!”

More karate chops. “Dass-dass-dass!!” he hisses, beyond words.

He smacks me in the ass then fades backward, leaving me to my agony. I ride on, but my quads are cooked, my breathing hoarse and ragged. I can’t get enough air. The pedals barely turn. Eventually, I wobble to the roadside and climb off my bike. It’s over.

“Okay, good job, Bill,” says Iñigo San Millán, PhD, calm and patient in his white lab coat as he brings an end to my fantasy.

I’m on a stationary bike in a carpeted office suite in South Denver,­ surrounded not by screaming Basque fans but by physical-­therapy patients trying to dodge my bodily fluids. San Millán is a well-known physiologist who has advised teams from ONCE to Garmin and now splits his time between research, work with the United Healthcare domestic squad, and advising private clients. The lactate-threshold test he just administered to me is one of the key ways he measures an athlete’s fitness.

You start pedaling easily on a stationary bike set up for a specific power output. Every few minutes, the resistance increases, and increases, and increases some more, until you can no longer keep going. San Millán structures the test by watts per kilogram, the key ratio when it comes to predicting success in cycling. I began at 1.5 watts/kg, or around 100 watts total.

At each increase, San Millán pricked my ear for a drop of blood, which a machine then analyzed for lactate, or lactic acid, the prime marker of muscular fatigue. I had a heart monitor strapped to my chest and a plastic mask clamped over my nose and mouth, directing my exhalations to another machine that broke down my oxygen use. All the data was streamed into a desktop computer, which plotted the sad graph of my physical condition.

After I recover, we meet in his office. San Millán has been administering this test to elite athletes for 15 years. Him giving it to the likes of me is the equivalent of Herbert von Karajan teaching Suzuki violin lessons to six-year-olds. In his whole career, says San Millán, one athlete stands out in particular, a young Spanish rider he tested almost 10 years ago. When the test got really hard, this rider stood up on the pedals, desperate. “Most of the time, that means the guy’s done, like in a minute or two,” San Millán says. This kid kept going out of the saddle for a full 25 minutes longer. His name was Alberto Contador, and his signature is on a yellow jersey in a frame behind San Millán’s desk.

To no one’s surprise, the results show that I’m no Contador. I never even stood on the pedals, and at one point I ripped the mask off because I felt like I couldn’t breathe. (“Everybody hates the mask,” consoles physiologist Allen Lim, who has worked for Garmin and RadioShack.) San Millán shows me that when I quit, I carried 7.2 millimoles of lactate per liter of blood—a tiny concentration that, nonetheless, made me feel like I was going to die.

“Contador would have been here,” San Millán says, pointing at another chart. I look more closely: It says 0.8. With a zero. “Like he was sitting on the couch, watching TV.”

Ouch. I sit quietly for a moment, awash in humility. Then I say the same thing everyone says when they finish a test like that, or a race, or even a tough climb. “I could have gone harder,” I say. “Totally could have gone harder.”

“YOU CAN ALWAYS go harder,” says Craig Lewis,­ on the phone from Boulder, Colorado. The 27-year-old American pro should know. He was riding a stellar Giro d’Italia last year when he slammed into a road sign, breaking four ribs, damaging a nerve in his right arm, and snapping his femur in two. Three months and seven surgeries later, he was back on his bike, riding in the U.S. Pro Cycling Challenge, a one-week stage race through the mountains of Colorado. He had barely trained at all by then, but he couldn’t afford not to race: His HTC-Highroad team was folding and he needed to prove himself to get a job for 2012.

Suffering is essential to the beauty and mystery of the sport. It gives the ride meaning. The greatest racers have a love of suffering that goes beyond any ratio of sacrifice to payoff.

He knew something wasn’t right. “I could barely put any kind of torque on the pedals,” he says. “I was basically riding with one leg.” Nearly every day, he would get dropped on the first climb, finding himself the last man on the road. Left on his own, he would grovel along, trying just to make it to the finish before the time cut. He flogged himself this way for nearly 800 miles, ending the race fifth from last, when ordinarily he might have expected to be in the top 10. Afterward, X-rays showed that his femur hadn’t fully healed, and that he was riding, essentially, on a broken leg.

While other sports have dramatic, thrilling, discrete moments—upper-deck home runs in baseball, Hail Mary passes in football, game-winning three-pointers in basketball—fans of cycling and other endurance sports such as running revel in witnessing ­extended bouts of suffering. Bike racing, the veteran mountain-bike champion Ned Overend has said, “is about pain.”

That’s what San Millán’s diabolical test was really measuring: my ability to endure pain, which may be just as important as my lactate threshold, my VO2 max, or any other physiological parameter. How long can you take it? Suffering is essential to winning races, but it’s just as important to charity riders­ tackling their first 25-miler or the commuter frantic to make the 9 a.m. Monday meeting. The hard truth of the sport is that you can’t achieve much, or get any better, without going through some pain—the ragged breathing, the burning legs, the oh-my-God-where-is-the-top desperation of a rider struggling on a long climb. “Suffering,” in the words of NBC commentator and ex-pro Bob Roll, “is the coin of the realm in cycling.”

On a deeper level, suffering is essential to the beauty and mystery of the sport. It gives the ride meaning. In fact, the word used to mean the same thing as “passion,” which stems from the Latin pati, to suffer. There are similarities. Anyone who has ever been in love knows that suffering is part of the experience at some point, and the greatest bike racers seem to have a love of suffering that goes beyond any reasonable ratio of sacrifice and payoff. “We think of it as delaying gratification for some reward,” says Lim, “but it’s never really about the reward; it’s about the moment, when you’re performing at your limit. And when it’s over, the only thing you want to do is get back out there again.”

To a true cycling fan, the greatest hero of last year’s Tour de France might not have been Cadel Evans, the workmanlike winner, but the gallant French rider Thomas Voeckler, who found himself in the yellow jersey early on, then managed to keep it for 10 days, hanging with more gifted riders through the toughest­ mountain stages. Voeckler was vividly proving a primal, puzzling truth: The “stronger” rider, in terms of pure physical ability, is not always the best. The bicycle allows you to ride as far into the dark realms of pain as you dare, which is where greatness is found, along with unlikely yellow jerseys.

“I’ve had very mediocre riders kick butt and make great careers,” says Colorado Mesa University coach Rick Crawford, a collegiate coach who has discovered talents like Tom Danielson, among others. “They take a 68 VO2 max and kick the crap out of the kid with a VO2 max of 85 because they’re smarter, they want it more, and they have an incredible will that can not be denied.”

That type of willpower is what let Voeckler hold off better ­riders for nearly two weeks, painfully and legendarily tearing himself to pieces until his body finally could give no more.

Or was his physical distress—like his willpower—all in his head? When you start to look into the precise nature of suffering—what it really is and how it relates to performance—things start to get pretty weird. In the last decade or so, the field of endurance-­sports science has been turned upside down and set on fire over the question of what, exactly, causes suffering, which scientists call “fatigue.” Some scientists are even questioning such bedrock concepts as VO2 max and lactate threshold, as well as the very notion that an individual’s physical performance has absolute, physiological limits. The lactate-threshold test? Meaningless, some experts say.

We’re not even sure anymore what suffering really represents, what causes it, and why some people seem to be so much better at enduring it than others. The old, purely physical view of suffering and fatigue—that your legs hurt because your legs hurt—is giving way to a much more complex model, where our performance, and our feelings of pain, and even what we think are our absolute physical limits, are all controlled by one fickle master: the brain.

ONE AUGUST MORNING in 1994, I showed up at Ski Liberty mountain resort, in southcentral Pennsylvania, to do my first mountain bike race. Alongside me was my closest riding buddy, Gaston. The two of us had been mountain biking ­together almost every weekend, and we had convinced each other to sign up for the beginner-class race—a couple 5-mile laps up, over, and around the 620-vertical-foot ski hill.

Calling Ski Liberty a “mountain resort” was as much a wishful exaggeration as labeling our riding habits “training.” On Sunday mornings we’d spend two or three hours banging around in the woods on our Cannondales, stopping to rest whenever we felt like it. On the way home, we would stuff our faces with Big Macs.

I had absurdly high hopes for myself. As race day drew near, I lulled myself to sleep with visions of crossing the finish line in triumph while my girlfriend cheered.

That dream exploded within the first mile, along with my lungs and my ego. At the gun, I joined 50 riders sprinting up Ski Liberty’s bunny slope in a cloud of dust. I’d done some tough mountain runs in college, but nothing had ever felt as bad as riding up that crappy little ski hill, not even the worst full-body sophomore-year hangover. As we crowded into the singletrack, bumping and shoving and crashing into each other, I wanted to crawl into the woods, lie down, and wait for sweet death.

Eventually, I made it over the top of the “mountain,” then descended shakily to the base area to begin the second lap. It didn’t take too many uphill pedal strokes to convince me that I didn’t need to be doing this to myself. I turned around and coasted down to the base, where my girlfriend was decidedly unimpressed. Her voice cooed a few words of sympathy for me, but her eyes said, “How hard can it be to ride a freaking bike?”

Gaston came around a few minutes later, his tongue flapping down around his navel, but he kept going to finish midpack, winning zero cash but priceless gloating rights. Lesson learned: The only thing worse than suffering is quitting.

But why did I quit, exactly?

Short answer: I wussed out. The slightly longer and more ­scientific answer starts with A.V. Hill, a British athlete-­scientist who’d run a 4:45 mile while in college and won the Nobel Prize in 1922 for research into how muscles produce heat. The year after that award, Hill and his colleagues at Manchester University began another study: They ran laps around an 85-meter grass track while breathing into an apparatus on their backs called the Douglas Bag, a primitive means of measuring oxygen consumption.

His seminal experiments showed that the faster he and his buddies ran, the more oxygen they used—but only up to a point. At a certain speed, their oxygen consumption plateaued. After that, they got very tired very fast, until they couldn’t continue. This, Hill reasoned, was because their muscles needed more oxygen than they could get. Without it, they were forced to function anaerobically, without oxygen, which quickly produced a lactic-acid overload—and the burning sensation that comes with ­intense ­exercise, such as my ignoble plod up the bunny slope. If the workload doesn’t decrease, the burn increases until the muscles­ ­become unable to function—like when I quit. Suffering, simply, is the pain of our body coming up against its physical limits.

Or so we used to think.

Seven decades after Hill and friends ran themselves dizzy, another athlete-scientist proposed that Hill’s model, which had been accepted as gospel by the entire field of exercise physiology, was actually dead wrong. Tim Noakes, a runner and former rower at the University of Cape Town, in South Africa, asked a simple question: If runners had to slow down and stop because their bodies ran out of oxygen, why didn’t more elite runners die from heart attacks? If runners at the top of the sport really were ­approaching the absolute limits of physiology, Noakes said, the extremely strong-willed athletes should be routinely killing themselves—literally running themselves to death. They weren’t, obviously. Moreover, he’d worked with heart patients and knew that even they could exercise safely (albeit slowly). So maybe, Noakes proposed in 1996, something forces us slow us down before bad things happen, in the same way that you cannot hold your breath until you die. Our bodies are engineered to maintain stability, or homeostasis, at all costs; when something threatens that stability, such as the effort involved in riding a bike up Mont Ventoux on a hot day, then some mechanism puts on the brakes. He called this mechanism the “central governor.”

Our bodies are engineered to maintain stability. When something threatens that stability, such as the effort of riding up Mont Ventoux, some mechanism puts on the brakes.

Noakes initially thought that the governor would be part of the muscles themselves, or possibly in the heart. He soon ­realized that it had to reside in the brain, which is responsible for activating or “recruiting” muscle fibers. When we turn the pedals on a bike, the brain triggers some muscle fibers—but not all. The governor works, Noakes says, by deciding how much muscle it wants us to use. Without a signal from the brain, a muscle won’t work. In tests, Noakes found that athletes at VO2 max were only activating half of the number of muscle fibers they used in a full-out sprint. So even though we think we’re at our physical limit, we might not be; the muscles just aren’t being allowed to operate.

To Noakes and his adherents, this explains an oft-observed phenomenon in running: In nearly all world-record performances in the 10K run, the last kilometer is the fastest. “Athletes always speed up at the exact time when they should be slowing down” under the old model, says Ross Tucker, who edits the ­Science of Sport blog and was a graduate student of Noakes’s. “That means there’s a reserve.”

So Craig Lewis is right: You really can always go harder. Except when you can’t, or shouldn’t—like in the heat. As it turns out, the central governor plays a crucial role in hot conditions. The reason runners and cyclists go slower in the heat is because the governor is protecting us. Studies of cyclists pedaling in hot rooms show that their effort tapers off well before body temperature reaches 104 degrees Fahrenheit, the point at which heatstroke sets in. Even in Olympic competition, athletes almost never exceed that limit.

One cyclist who famously crossed the line is Tom Simpson, the British rider who collapsed near the top of Ventoux on a very hot day in the 1967 Tour de France. He had large quantities of amphetamines in his system, so his death is generally attributed to doping,­ but the real reason he died was because the amphetamines had switched off his brain’s inhibitions. The drugs had ­silenced his central governor, allowing him to ride himself to death. “He was able to go beyond what his brain said was acceptable,” says Tucker. “Amphetamines lifted that ceiling, and he died.”

In typical conditions, our ceiling is well below the point of death. We might think we’re going to die, but we’re not even close. Tucker has done studies showing that cyclists riding in a hot room will slow down; but if those same cyclists are merely told the room is going to be hot, when it actually isn’t, they slow down in anticipation of the effects of the heat. “The performance impairments happen before they start,” says Tucker. “The brain goes, hold on, pace yourself.”

But it’s also possible to trick the brain into letting you go faster. In a recent study from Northumbria University in England, scientists had cyclists ride as hard as they could for 4,000 meters, about a five-minute all-out effort. They did this two times, to establish a personal best. Then they raced against a computer-generated avatar that they were told represented their own best effort. In fact, the avatar was going 1 percent faster. And every rider caught his avatar.

Even stranger, cyclists who merely taste a sweet energy drink, but don’t swallow it, will ride faster because the brain expects a shot of carbohydrate fuel.

In another telling study, runners were subjected a variant of the standard ramp-up VO2 max test, in which the intensity is increased ­until the subject can’t continue. (Imagine riding a stationary trainer harder and harder until you puke, and you’ll get an idea what a VO2 max test feels like.) This has been the accepted method for decades. This time, the scientists turned the protocol upside down, so the test started harder, then got progressively easier. In every case, the runners began and sustained efforts at well above their supposed max.

I DIDN'T COMPETE for a long time after the Ski Liberty debacle. Racing, I decided, was a great way to ruin a bike ride. Then Gaston signed us up as part of a team for a 24-hour race, and I couldn’t weasel out of it. In the weeks before the event, dread consumed me. When I got on course for my first lap, though, I was a different rider. This time, if I quit I would be letting down the whole team, not just myself. Plus, I’d had it with Gaston’s gloating. I had to handle the pain. To my surprise, I passed people on the climbs and let my wheels run on the downhills. My only thought was to go as fast as I could, all the time, and it hurt like hell—and I loved it.

I got hooked. Soon I was mountain-bike racing ­almost ­every weekend, subjecting myself to two hours of full-on, lactate-threshold suffering each time. I began the season as a sport-class straggler, worked my way to the middle of the pack, and by the following year was notching top-10 finishes before upgrading to ­Expert. The suffering never lessened—the burning legs, the hyperventilating, the thoughts of quitting. As Greg ­LeMond quipped: “It never gets easier. You just go faster.” Once in a hot race when I was going as hard as I possibly could, I looked down at my heart monitor and saw a blinking, and terrifying, 212. My solution was to stop wearing the monitor in races. The pain was still pain—it hurt—but rather than shrink from it, I chased the feeling of burning muscles, the taste of blood in my throat that comes from extreme effort. It was purifying, cathartic.

“Some people, nonathletes, immediately move away from those kinds of sensations,” says Julie Emmerman, PsyD, a ­Boulder-based psychotherapist who has raced mountain bikes and road bikes professionally and specializes in training athletes—cyclists in particular. “That’s a fear-based reaction. Whereas an athlete will say, ‘I’m familiar with this, and I can deal with it.’”

For Emmerman, it starts with labeling: “You keep saying ­‘suffering,’” she chides me by phone from New Mexico, where she is racing the Tour of the Gila. “I call it ‘physical discomfort.’”

Like Emmerman, other professional riders all seem to have their own strategies for coping with the sensation. Jens Voigt, often seen on the front of the peloton with the face of a man whose toenails are being plucked out with hot pliers, relies on a Teutonic mantra: “Shut up, legs!” Lewis feels his greatest enemy isn’t the pain in his legs, but his brain and its expectations. “If you get to the limit where you thought you would give up, your body shuts down,” he says. “You’ve already convinced yourself, that’s it.”

In retrospect, that’s what happened to me when I took San Millán’s test. I figured I had to make it to about 3.5 watts per kilogram to avoid undue ridicule from the readers of BICYCLING—almost as if giving myself permission to quit there.

Lewis’s approach to managing his suffering is to imagine folding it up then sticking it into one of the pockets on the back of his jersey. “If you keep going,”he says, “it can be almost not a big deal to go through it. Then keep going up the next switchback, then worry about the next kilometer. The pain kind of subsides after a certain point.”

Other riders devise more elaborate scenarios. At the Tour of California one year, I rode in a team car behind Garmin rider Dave Zabriskie during the Solvang time trial. Zabriskie is one of the best time-trialists precisely because he has an inhuman ability to force himself to suffer. But his coaches said not one word to him throughout the 30-minute effort; there was no yelling, no “Venga! Venga!” Just radio silence.

Once in a hot race when I was going as hard as I possibly could, I looked down at my heart monitor and saw a blinking, and terrifying, 212. My solution was to stop wearing the monitor in races.

“Dave doesn’t want any information,” explained Allen Lim, who was then Garmin’s team physiologist. Zabriskie’s suffering all takes place internally, measured to his own feedback, ­although he’s not exactly alone in there. “When he’s in a time trial,” Lim said, “he thinks of himself as a superhero.”

The common factor in all the approaches is focus: If you’re asking grand existential questions, you’re in trouble, which might be why poets don’t make good bike racers, and vice versa.

But there are also rare times when suffering—sorry, “physical discomfort”—just seems to vanish entirely: when you’re perfectly trained, and you’re on top of the gear and far from thoughts of surrender and defeat. Emmerman says her patients describe it as a zone of total detachment, where the body’s feelings of pain barely even register in the consciousness. “That’s the zone you want to be in,” says Zabriskie’s teammate Christian Vande Velde. “You drain out all the fans, everything, even the director; and it’s everything that you’ve trained yourself to do for the last 20 years of your life, and you’re just pretty much on autopilot.”

Vande Velde is legendary for mediocre performances in fitness tests—and killing it in races. “The physiologists would look at his numbers and say, ‘I don’t know how this guy finishes top 20 in the Tour,’” says Jonathan Vaughters, his team director. Yet there he was in the 2008 Tour de France, in third place after two weeks, right behind Cadel Evans and ahead of both Schleck brothers. Then came the crucial first day in the Alps, which finished on a sharp climb. When the pack hit the base of the climb, 100 guys suddenly became 12, then eight. Vande Velde was right there. He followed the wheels, swinging across the road to cover ­everything. “You had to follow the attacks all the way, pushing yourself so far,” he says. “When somebody attacks, you just jump.”

When he got to the top, the finish, he sat there for 15 minutes, straddling his bike and digesting what had happened. It took a while before he felt ready to ride back down to the base, where the team buses waited. He’d slipped a spot in the overall standings, to fourth, but he had dropped Evans and he knew now that he could hold his position all the way to Paris. It was the best racing day of his life, and he barely felt—or saw—a thing.

“Coming down the hill,” he remembers, “I’m like, holy crap, where did all these people come from? There were half a million people on the hill that day, and I hadn’t seen a single one of them.”

BUT IF SUFFERING can simply disappear like that, like it did for Christian Vande Velde, then what is it, really? An experience like that seems to imply that suffering is more complex than either physical limits or a central governor.

Among scientists, the debate between proponents of “central” and “peripheral” fatigue is as nasty as it is unresolved. An editorial in the journal Sportscience sneered at “The Improbable ­Governor,” while in a 2009 issue of Sports Medicine, Noakes’s most ­vocal opponent, Roy Shephard, MD, PhD, published an article wondering, “Is It Time to Retire the ‘Central Governor’?”

In a rebuttal letter, Noakes shot back that doing so would result in a “brainless model of exercise physiology.” With a sigh, he tells me, “If an idea has been taught 80 or 90 years, it’s not going to go away immediately just because some South African guy comes along and says it’s wrong.” But about that lactate-threshold test? That had to measure something, right? “Nothing meaningful at all,” he says definitively. “The human body is so complex you can’t reduce it to single numbers, and say you have to train at a heart rate of 140. It’s rubbish. Kenyans don’t know what their VO2 max is. They don’t bother. They train to win; they train to beat the person next to them.”

We’re no closer to knowing the truth about suffering than ­Supreme Court Justice Potter Stewart got in his famous description of pornography: We can’t define it, but we know it when we see it.

All that’s needed to settle the issue is some evidence. But that’s the problem. To prove the existence of a central governor, scientists need to see inside an athlete’s brain, to determine which regions light up during exercise, and to observe the governor’s role in activating (or not activating) muscle. We can’t do that yet, because you can’t ride a bike in an MRI machine. A scientist in Texas is working on a kind of portable MRI that could be worn by someone who is exercising, but it’s not ready yet. “We’ve hit a little bit of a dead end,” admits Ross Tucker. “The [central governor] model has moved to this model that couldn’t really be tested. Which isn’t really good science.”

Muscle is just as much of a black box as the brain. Science doesn’t really know what goes on inside our muscles when we exercise, only that it is far more complex than we realize. We now know that lactic acid is not the only reason our muscles stop working; in fact, well-trained athletes can actually recycle it into a kind of fuel. There are also things called “leaky calcium channels,” that stop muscles from contracting properly. Neurotransmitters and free-radical damage also seem to play important roles, along with other processes we still don’t completely fathom.

The only way to thoroughly document what happens during exercise is via muscle biopsy, which entails making an 1-inch incision in the subject’s leg then slicing down an inch deep to extract muscle tissue. The wound alone takes a month to heal, which is why you don’t see any Tour de France cyclists volunteering. Plus, for the results to have any meaning, you’d have to perform the procedure immediately after a sufficiently taxing effort, such as on the finish line atop Alpe d’Huez. The lactate test, which is easier to perform, offers only some knowledge. “Lactate is not solely responsible,” says San Millán. But, he says, “it is an ­excellent ­biomarker.” Over his career, he has collected biomarkers from hundreds of elite athletes, building a unique database; most ­published

"The human body is so complex you can't reduce it to single numbers," says Noakes. "Kenyans don't know what their VO2 max is. They train to win; they train to beat the person next to them."

studies rely on amateur cyclists or college-­student ­volunteers. Among scientists, this makes San Millán a kind of connoisseur of high-level suffering. One thing he’s discovered is that even at the most rarefied level of cycling, quantum leaps in physical performance still ­exist between midpack pros and race winners—and it’s not the winners who suffer most but the sprinters­ trying to haul themselves over the Alps, the climbers struggling through time trials. That’s where pain reaches its peak, he thinks—far from the podium, deep in the trenches of the sport. Those are the athletes who are pushing the limits the hardest.

And where do those limits originate? He acknowledges a role for the brain. But, he says, “What happens in the cell governs everything upstream. Mental toughness can only take you so far. You can be the toughest driver in the world, and if you only have a Citroen”—he shoots me a look—“you cannot beat a Ferrari.”

MAYBE SAN MILLÁN is right. But maybe that doesn’t mean Noakes is wrong, either. In fact, they agree on one major point: “The person who does the best is the one who suffers the least, not the most,” Noakes says.

The Iron Cross is a 62-mile cyclocross race in and around Pennsylvania’s hilly Michaux State Forest that mixes long dirt-road climbs, fast pavement sections, technical singletrack, and a 500-vertical-foot run-up under a power line.

Though I no longer race with the frequency or intensity I once brought to the sport, I signed up for the Iron Cross last fall. I’d done it once before, back when I had a coach and a training program, and I actually woke up early to go do intervals before work. I’d finished in just over five hours that first time, respectably midpack. This time, I wasn’t training beforehand, just riding regularly and enjoying myself. I decided there was no way I could legitimately race Iron Cross, but that it would be cool to ride around the course in six hours or so.

When race day came, it felt more fun than torturous. There’s a big climb toward the end called Woodrow that killed me during that first race; I lost maybe 25 places in a few miles. This time around, I knew what to expect. I knew the road, where it curved, where it got steep, and I was able to sort of pack up the suffering and dose it out when I needed to.

I was still hurting myself—in the coming weeks, I’d be more sore than I’d ever felt after a race—but in the moment, I kept going, staying with much stronger and better-trained racers. I passed five guys in the last 5 miles, and when I crossed the finish line, I saw something that convinced me, once and for all, that the key to suffering lies somewhere in between the body and the brain. It was the clock. It didn’t say six hours, as I had expected, but 5:07.

your body would switch from the aerobic production of power to anaerobic, which is a short-term state of operation and also more painful. This is the hardest intensity you could maintain for an extended time. You should be able to spit out a sentence or two, but probably have to break between phrases for a breath.

10

90% To 1000%
of Max

121% to 150%
of FTP

You're working at a rate you know you can't hold for more than a minute or so—or perhaps even a few seconds at a full-out effort. You cannot speak, though you might scream an obscenity or wail like a beast.

You're in the final 30" of a fight with Philo Beddoe.

11

12

+150%
of FTP

Your at or near your VO2 max, at the point which you body can no longer process enough oxygen to function—this is your max effort.

The orangutan knocked you out.

* Rate of Perceived Exertion is a scale based on the subject's own perception of how difficult an effort is, from 1 (very light) to 12 (maximum exertion).

** Heart Rate is based on percent of maximum beats per minute.

*** Power Output is based on percentage of Functional Threshold Power (FTP), which is the wattage you would average with the hardest possible efforts over the course of a 60-minute race